1. Field of the Invention
The present invention relates to optical fiber cables more particularly, to optical fiber cables in which the optical fibers are imbedded in a matrix material.
2. Description of the Prior Art
Optical fiber cables have been used for the past several years to transmit information at high rates and long distances. The transmission medium is composed of hair-thin optical fibers which are protected from external forces by precisely designed and manufactured cable structures. One such cable is a structure in which all of the optical fibers are in a single, centrally located, gel filled buffer tube. This cable structure can incorporate additional protection which may consist of radially applied strength members, corrugated armor and plastic sheaths. An example of such a single buffer tube structure is shown in U.S. Pat. No. 5,029,574.
In order to simplify construction, installation and maintenance of optical fiber cable, the individual optical fibers are now being held in a planar array called an optical fiber ribbon. In an optical fiber ribbon, a plurality of optical fibers, typically twelve, are held in precise parallel positions in the planar array. The array of optical fibers are held together with an adhesive matrix material such as an ultra-violet curable coating material as disclosed in U.S. Pat. No. 4,900,126. Since the optical fibers are precisely fixed in the ribbon structure, simultaneous mass splicing of the optical fibers can be readily accomplished.
In addition, it has been increasingly desirable to design optical fiber cable structures using all dielectric materials. One example of an all dielectric cable using optical fiber ribbons is produced by the American Telephone and Telegraph Company (AT&T). The AT&T dielectric cable is comprised of optical fiber ribbons, buffer tube filling compound, a polyethelyne tube, water swellable tape, two fiberglass reinforced plastic strength rods, four fiberglass yarn fillers, and a high-density polyethelyne jacket. The AT&T cable requires the longitudinal application of four fiberglass yarns and two fiberglass reinforced plastic strength rods over a water swellable tape to provide for a torsionally flexible cable which meets the customer specification for water flow ingress. The AT&T design utilizes a water swellable compound system which absorbs water. A complete water swellable system absorbs a much larger quantity of water, as compared to a gel filled system, holding the water in place, and allowing an increased level of moisture attack on the other cable materials over time. The moisture may cause mechanical damage to the cable materials when the water freezes at temperatures of 32.degree. F. or below.
Previous attempts to make a gel filled cable utilizing optical fiber ribbons have proved unsuccessful due to poor torsional flexibility and operator handleability.